Hello and welcome to Apple Support Communities, mabblemedia.
If we understand your post correctly, your iPhone is being treated like an unknown or new device when connected to your computer even though you've backed up your iPhone to this computer previously. We’d like to help.
It looks like your existing backup is still saved and available. Select set up as new device from this screen. This will not erase your iPhone. It will simply tell your computer to handle this device as if it were the first time it had been connected. You'll then be able to sync or create a new backup of your iPhone.
Follow the steps in this article:
How to back up your iPhone, iPad, and iPod touch
Let us know if that resolves this issue for you.
Thanks for using the Apple Support Communities.